1. Field of the Invention
The present invention relates to a liquid-repellent member, a liquid-jet head using the same, and a liquid-jet apparatus.
2. Description of the Related Art
A liquid-jet head has a nozzle plate in which a large number of fine eject holes (nozzle orifices) for ejecting a liquid therefrom are formed at minute spaced intervals. When ejected from the eject holes, ink may adhere to an ejecting surface. In this case, when ink next ejected comes into contact with adhered ink remaining on the ejecting surface, an ejecting path for the next ink droplets ejected is curved under influence of surface tension, viscosity or other properties of the adhered ink. Thus, the adhered ink remaining on the ejecting surface causes a problem of making it impossible to perform printing in a predetermined spot. Techniques for solving this problem include a technique of providing a liquid-repellent film on the jet surface of the nozzle plate for a purpose of preventing adhered ink from remaining on the ejecting surface (see Japanese Patent Laid-open Official Gazette No. 2004-351923).
When the liquid-repellent film is provided on a solid surface such as the nozzle plate, a contact angle of a liquid (usually water) is generally, taken as an index of liquid repellency of the solid surface. Moreover, high alkali resistance is required for long-term use because ink is often alkaline. Evaluation of durability of the liquid repellency (hereinafter referred to as “liquid-repellent durability”) involves, for a long period of time, dripping a liquid onto the solid surface, exposing the liquid thereon, or subjecting the solid surface to mechanical friction; measuring the contact angle; and evaluating the liquid-repellent durability according to whether the measured value is high or low (see “The latest trends in high-water-repellent techniques from the ultra-water-repellent materials to the latest applications thereof,” TORAY Research Center, Inc., Oct. 1, 2001, pp. 20-21, for example).
However, the contact angle does not indicate only the liquid repellency of the solid surface, because the contact angle varies according to not only the liquid repellency but also interaction among characteristics of a liquid such as a type, concentration or temperature thereof, and a state of the solid surface such as chemical factors or physical structural factors of its topmost surface. Moreover, even if the contact angle is changed by contamination on the solid surface, when a level of the contamination is a trace and invisible, the contact angle value may be misinterpreted. Therefore, there is a case where the liquid repellency or liquid-repellent durability may be often low although the result of evaluation based on the contact angle shows that the liquid repellency or liquid-repellent durability is good. It has been difficult to stably supply a member having excellent liquid repellency and liquid-repellent durability.